1. Field of the Invention
Embodiments of the present invention relate generally to medical devices and methods. More particularly, embodiments of the present invention relate to the structure and deployment of a segmented stent at a luminal os at a branching point in the vasculature or elsewhere.
Maintaining the patency of body lumens is of interest in the treatment of a variety of diseases. Of particular interest to the present invention are the transluminal approaches to the treatment of body lumens. More particularly, the percutaneous treatment of atherosclerotic disease involving the coronary and peripheral arterial systems. Currently, percutaneous coronary interventions (PCI) often involve a combination of balloon dilation of a coronary stenosis (i.e. a narrowing or blockage of the artery) followed by the placement of an endovascular prosthesis commonly referred to as a stent.
A major limitation of PCI/stent procedures is restenosis, i.e., the re-narrowing of a blockage after successful intervention typically occurring in the initial three to six months post treatment. The recent introduction of drug eluting stents (DES) has dramatically reduced the incidence of restenosis in coronary vascular applications and offers promise in peripheral stents, venous grafts, arterial and prosthetic grafts, as well as A-V fistulae. In addition to vascular applications, stents are being employed in treatment of other body lumens including the gastrointestinal systems (esophagus, large and small intestines, biliary system and pancreatic ducts) and the genital-urinary system (ureter, urethra, fallopian tubes, vas deferens).
Treatment of lesions in and around branch points generally referred to as bifurcated vessels, is a developing area for stent applications, particularly, since 10% of all coronary lesions involve bifurcations. However, while quite successful in treating arterial blockages and other conditions, most stent designs are challenged when used at a bifurcation in the blood vessel or other body lumen. Presently, many different strategies are employed to treat bifurcation lesions with currently available stents all of which have major limitations.
One common approach is to place a conventional stent in the main or larger body lumen over the origin of the side branch. After removal of the stent delivery balloon, a second wire is introduced through a cell in the wall of the deployed stent and into the side branch. A balloon is then introduced into the side branch and inflated to enlarge the side-cell of the main vessel stent. This approach can work well when the side branch is relatively free of disease, although it is associated with increased rates of abrupt closure due to plaque shift as well as increased rates of late re-restenosis.
Another commonly employed strategy is the ‘kissing balloon’ technique in which separate balloons are positioned in the main and side branch vessels and simultaneously inflated to deliver separate stents simultaneously. This technique is thought to prevent plaque shift.
Other two stent approaches including Culotte, T-Stent and Crush Stent techniques have been employed as well. When employing a T-stent approach, the operator deploys a stent in the side branch followed by placement of a main vessel stent. This approach is limited by anatomic variation (angle between main and side branch) and inaccuracy in stent positioning, which together can cause inadequate stent coverage of the sidebranch os. More recently, the Crush approach has been introduced in which the side-vessel stent is deployed across the os with portions in both the main and side branch vessels. The main vessel stent is then delivered across the origin of the side branch and deployed, which results in crushing a portion of the side branch stent against the wall of the main vessel. Following main-vessel stent deployment, it is difficult and frequently not possible to re-enter the side branch after crush stenting. Unproven long-term results coupled with concern regarding the inability to re-enter the side branch, malaposition of the stents against the arterial wall and the impact of three layers of stent (which may be drug eluting) opposed against the main vessel wall has limited the adoption of this approach.
These limitations have led to the development of stents specifically designed to treat bifurcated lesions. One approach employs a stent design with a side opening for the branch vessel which is mounted on a specialized delivery balloon. The specialized balloon delivery system accommodates wires for both the main and side branch vessels. The system is tracked over both wires which provides a mean to axially and radially align the stent/stent delivery system. The specialized main vessel stent is then deployed and the stent delivery system removed while maintaining wire position in both the main and side branch vessels. The side branch is then addressed using kissing balloon or by delivering and an additional stent to the side branch. Though this approach has many theoretic advantages, it is limited by difficulties in tracking the delivery system over two wires (Vardi et al, U.S. Pat. Nos. 6,325,826 and 6,210,429).
Another approach, of particular interest to the present invention, includes the use of fronds, or fingers extending from the scaffolding of a side branch stent to facilitate positioning of the stent at a bifurcated lesion. This approach is described in detail in co-pending commonly assigned application Ser. No. 10/807,643 the full disclosure of which is incorporated herein.
However while above approach has significant promise, conventional stent delivery systems, such as balloon catheters, can have difficulty managing the fronds during delivery. In such conventional systems, the stent is usually crimped onto the balloon of the balloon catheter. While fine for many conventional stent designs, conventional balloons systems may not always prevent the fronds on a stent from separating from the balloon as the catheter is advanced through curved portions of the vasculature, such as those found in the circumflex coronary artery.
For these reasons, it would be desirable to provide improved systems and methods for delivering stents, particularly stents with fronds or other protruding anchoring elements at one end, to treat body lumens at or near the location of an os between a main body lumen and a side branch lumen, typically in the vasculature, and more particularly in the arterial vasculature. It would be further desirable if such systems and methods could treat the side branch vessels substantially completely in the region of the os and that the prostheses in the side branches be well-anchored at or near the os.
2. Description of the Background Art
Stent structures intended for treating bifurcated lesions are described in U.S. Pat. Nos. 6,599,316; 6,596,020; 6,325,826; and 6,210,429. Other stents and prostheses of interest are described in the following U.S. Pat. Nos. 4,994,071; 5,102,417; 5,342,387; 5,507,769; 5,575,817; 5,607,444; 5,609,627; 5,613,980; 5,669,924; 5,669,932; 5,720,735; 5,741,325; 5,749,825; 5,755,734; 5,755,735; 5,824,052; 5,827,320; 5,855,598; 5,860,998; 5,868,777; 5,893,887; 5,897,588; 5,906,640; 5,906,641; 5,967,971; 6,017,363; 6,033,434; 6,033,435; 6,048,361; 6,051,020; 6,056,775; 6,090,133; 6,096,073; 6,099,497; 6,099,560; 6,129,738; 6,165,195; 6,221,080; 6,221,098; 6,254,593; 6,258,116; 6,264,682; 6,346,089; 6,361,544; 6,383,213; 6,387,120; 6,409,750; 6,428,567; 6,436,104; 6,436,134; 6,440,165; 6,482,211; 6,508,836; 6,579,312; and 6,582,394.